1. Field of the Invention
The present invention relates to automatic tool changing method and device for automatically changing tools to be used in a machine tool, and in particular to automatic tool changing method and device for a machine tool controlled by a numerical controller.
2. Description of Related Art
An automatic tool changer for use in a CNC drill of a machine tool controlled by a numerical controller is designed to use the reciprocal vertical motion of a spindle on which the drill is mounted to replace a tool mounted on the spindle with a tool held in a turret. In order to shorten the time required for tool exchange as well as to lessen the impact that occurs during tool exchange, moving the turret in the same direction as the direction in which the spindle head moves when the turret swings to move toward and retreat from the spindle during tool exchange so as to reduce the difference in the relative velocities of the turret and the spindle and thereby lessen the impact is known (JP 2535479B).
There is also known a tool changer in which a plurality of grip arms for gripping tool holders are provided in a tool magazine so that each of grip arms is swung utilizing an axial motion of the spindle so that a tool holder attached to the spindle is changed with a desired one, and a velocity of the axial motion of the spindle is reduced in a region of performing the tool change so as to reduce an impact of a mechanical collision of the tool holder and the grip arm during the swing motion of the grip arm (see JP 2006-272473A).
FIG. 11 is a schematic diagram of the automatic tool changer described in JP 2535479B that lessens the impact attendant upon tool exchange when changing tools.
The automatic tool changer is comprised of a turret 38 provided at the end of an arm member 2. The turret 38 has a plurality of grips 28 around its outer periphery, and with these tools the turret 38 holds tools. The turret 38 is equipped with a decelerator device 39 for selecting a desired tool by an allocation movement, so as to decelerate the rotation input via a turret gear 30 that engages a spindle gear 32 of the spindle and rotate the turret 38. The turret 38 holds a tool holder 36 via the plurality of grips 28. A crank 4 is fixedly mounted on the rear surface of the turret 38.
The spindle head 34 is designed so as to be reciprocally movable vertically (along the Z-axis) along a support column 1. On the spindle head 34 are provided a swing cam CS that rotates and swings the crank 4 and the turret 38 about a pivot shaft 18 and a lift cam CL for raising and lowering the crank 4 and the turret 38. The swing cam CS is comprised of a straight portion CSa, a curved portion CSb and then another straight portion CSc. The lift cam CL is comprised of a straight portion CLa and a curved portion CLb.
One end of the crank 4 is rotatably supported on the pivot shaft 18 and the other end is rotatably attached to a swing roller 21 that cooperates with the swing cam CS. An urging means 26 is attached to the center of the crank 4, and the crank 4 is urged counterclockwise around the aforementioned pivot shaft 18 shown in FIG. 11. In other words, the swing roller 21 is pressed against the cam surface of the swing cam CS by the urging means 26.
The pivot shaft 18 is connected to a lift slider 16 that is constructed so as to be able to move reciprocally vertically along a linear guide 40 that is fixedly mounted on the arm member 2. A lift link 14 is mounted on the other end of the lift slider 16. The lift link 14 is constructed so as to move reciprocally vertically as a single unit with the lift slider 16. A lift lever having two lift lever arm members 6, 8 and rotatable about a rotary shaft 10 is rotatably attached to the other end of the aforementioned lift link 14. The rotary shaft 10 is horizontally attached to the arm member 2, such that the lift levers 6, 8 are attached so as to be rotatable about the rotary shaft 10. A lift roller 22 that engages the lift cam CL is rotatably attached to the end of the lift lever 6. The lift roller 22, by engaging the lift cam CL, moves the lift link 14 and the lift slider 16 up and down in the drawing, which moves the turret 28 up and down.
The spindle head 34 is driven by a Z-axis servo motor 41. FIG. 11 shows the spindle head 34 raised and in a tool exchange state. During machining, the spindle head 34 is lowered and the swing roller 21 contacts the straight portion CSa of the swing cam CS, the crank 4 and the pallet 38 are rotated counterclockwise about the pivot shaft 18 from the state shown in FIG. 11, and the turret 38 is held in a state of retreat from the spindle. In addition, the lift roller 22 also contacts the straight portion CLa of the lift cam CL.
When a tool change order is input in the machining state, the Z-axis is driven by the Z-axis servo motor 41, the spindle head 34 starts to ascend, and the swing roller 21 moves to a swing cam CS swing starting position, that is, the starting point of the curved portion CSb. At this point, the Z-axis (the spindle head 34) stops and the orientation of the spindle starts. Then, when orientation finishes, the Z-axis (spindle head 34) once again starts to ascend. The ascent of the Z-axis (spindle head 34) moves the swing roller 21 over the curved portion CSb of the swing cam CS and the turret 38 starts to swing counterclockwise around the pivot shaft 18. The curved portion CSb of the swing cam CS is shaped so that the end of the grip 28 moves toward a V groove in the tool holder 36 without contacting the spindle gear 32 of the spindle, and a roller provided at the end of the grip 28 moves accurately over the V groove after the roller engages the V groove.
The ascent of the Z-axis (spindle head 34) causes the swing roller 21 to pass over the curved portion CSb and move to the straight portion CSc, where the swing movement ends.
By contrast, during deceleration of the swing, the lift roller 22 engages the curved portion CLb of the lift cam CL, causing the lift levers 6, 8 to rotate clockwise about the rotary shaft 10, raising the lift link 14 and the lift slider 16, and causing the crank 4 and the turret 38 to accelerate in the same direction as the ascent of the Z-axis (spindle head 34). As a result, toward the end of the swing movement, the turret 38 ascends with the Z-axis (spindle head 34) so that the difference between their relative velocities is zero and no impact occurs.
After the swing is finished, the Z-axis (spindle head 34) is fast forwarded so as to rise to an allocation point and simultaneously the turret 38 starts a lift movement for detaching the tool holder 36 from the spindle. The swing roller 21 moves over the flat portion CSc of the swing cam CS and the lift roller 22 moves back toward where it started from the peak position of the curved portion CLb, causing lift acceleration in the opposite direction of the direction in which the spindle head 34 moves (ascends). As the swing ends, the crank 4 and the turret 38 move under the spindle head 34, detaching the tool holder 36 from the spindle.
After the Z-axis (spindle head 34) has ascended, and in a state in which the spindle gear 32 and the decelerator device 39 turret gear are engaged, the spindle rotates and allocation of the desired tool is executed. After turret allocation is finished, the Z-axis (spindle head 34) descends along the Z-axis in reverse order of the procedure described above. Therefore, when the spindle takes the tool holder 36 from the grip 28, the relative velocity of descent of the Z-axis (spindle head 34) and the turret 38 is substantially zero. With the end of the return swing of the turret 38 the spindle head 34 returns to its original position and tool exchange is completed.
FIGS. 12a and 12b are diagrams of the movement velocity patterns (velocity diagram) of the Z-axis (the spindle head 34) (FIG. 12a) and of the turret 38 swing. FIGS. 12a and 12b show changes in velocity from the start of the swing of the turret 38 as the Z-axis (spindle head 34) ascends to descent of the Z-axis (spindle head 34) and the end of the swing.
As shown in FIGS. 12a and 12b, in the conventional tool changer, while the swing of the turret is being executed, the Z-axis (spindle head 34) is moved at a relatively low constant velocity. By changing the movement of the Z-axis (spindle head 34) with the vertical movement of the lift slider that supports the turret 38 with the lift cam CL so as to cause the turret 38 to move in the same direction as the Z-axis (spindle head 34), the relative velocity of the Z-axis (spindle head 34) and the turret 38 can be reduced to substantially zero, so that no impact arises at the end of the swing of the turret 38.
In the conventional automatic tool changer constructed so that no impact arises from tool exchange as described above, when the turret 38 is swung and either moved toward or retreated from the spindle, a cam structure is required that moves the turret vertically relative to the spindle head 34 and reduces the relative velocity of the turret 38 and the spindle head 34 (to zero difference in velocity) so as to lessen the impact. Specifically, the lift lever 8, the lift link 14, the lift slider 16, the lift roller 22, the linear guide 40 and the lift cam CL are required. However, machine tools generate dust when machining, and since this dust adheres to the cam groove (CL) the cam groove (CL) head must be cleaned. If this cleaning is inadequate, or if the lift roller 22 is insufficiently lubricated, friction between the cam groove (CL), the lift roller 22 and the like is sometimes generated. In such cases, the turret 38 looses its smooth swing and as a result the cam and the lift roller must be replaced.
Further, the cam mechanism (the lift lever 8, the lift link 14, the lift slider 16, the lift roller 22, the linear guide 40 and the lift cam CL) for raising and lowering the turret 38 described above has the disadvantage that it complicates the tool changer mechanism as a whole, increasing the cost of parts as well as assembly.